//! Overflows the stack and passes if the double-fault handler (running on
//! its own IST stack) gets control instead of the CPU triple-faulting.
#![no_std]
#![no_main]
#![feature(abi_x86_interrupt)]

use core::panic::PanicInfo;
use lazy_static::lazy_static;
use rust_kernel::{QemuExitCode, exit_qemu, serial_print, serial_println};
use x86_64::structures::idt::{InterruptDescriptorTable, InterruptStackFrame};

#[unsafe(no_mangle)]
pub extern "C" fn _start() -> ! {
    serial_print!("stack_overflow::stack_overflow...\t");
    rust_kernel::gdt::init();
    TEST_IDT.load(); // our own IDT whose double-fault handler reports success
    stack_overflow();
    panic!("Execution continued after stack overflow");
}

#[allow(unconditional_recursion)]
fn stack_overflow() {
    stack_overflow(); // each call pushes a return address
    unsafe { core::ptr::read_volatile(&0u8) }; // prevent tail-call optimisation
}

lazy_static! {
    static ref TEST_IDT: InterruptDescriptorTable = {
        let mut idt = InterruptDescriptorTable::new();
        unsafe {
            idt.double_fault
                .set_handler_fn(test_double_fault_handler)
                .set_stack_index(rust_kernel::gdt::DOUBLE_FAULT_IST_INDEX);
        }
        idt
    };
}

extern "x86-interrupt" fn test_double_fault_handler(
    _stack_frame: InterruptStackFrame,
    _error_code: u64,
) -> ! {
    serial_println!("[ok]");
    exit_qemu(QemuExitCode::Success);
    rust_kernel::hlt_loop();
}

#[panic_handler]
fn panic(info: &PanicInfo) -> ! {
    rust_kernel::test_panic_handler(info)
}